The present invention relates to disc drive storage devices. More particularly, the present invention relates to cushions placed on head suspensions of a disc drive to provide enhanced shock protection to the head by limiting vertical excursions and dampening motion of the suspension and the attached head.
FIG. 1 illustrates a typical computer disc drive 20 that includes one or more discs 22 mounted on a hub 24 for rotation about a spindle axis 25 (FIG. 2). The discs 22 are typically coated with a magnetic medium for storage of digital information in a plurality of circular, concentric data tracks. A spindle motor rotates the hub 24 and the attached discs 22 about the axis 25 to allow a head or xe2x80x9csliderxe2x80x9d 26 carrying electromagnetic transducers to pass over each disc surface and read information from or write information to the data tracks.
The slider 26 is typically formed from a ceramic block having a specially etched air bearing surface that forms an air xe2x80x9cbearingxe2x80x9d as the disc rotates beneath the slider. The hydrodynamic lifting force provided by the air bearing surface causes the slider 26 to lift off and xe2x80x9cflyxe2x80x9d a very small distance above the surface of the disc 22 as the disc spins up to its operating speed. Although the fly height of the slider 26 is only a fraction of a micron, this thin film of air between the slider 26 and the disc 22 prevents damage to the fragile magnetic coating on the surface of the disc.
The slider 26 is preferably moved between data tracks across the surface of the disc 22 by an actuator mechanism 28 such as a rotary voice coil motor. The actuator 28 includes arms 30 (FIGS. 1 and 2) attached to each of the sliders 26 by flexible suspensions 32. Each suspension 32 essentially comprises a flat sheet metal spring that exerts a controlled preload force on the slider 26 in the vertical direction (i.e., against the surface of the disc 22 as shown in FIG. 2). The preload force supplied by the suspension 32 effectively counters the hydrodynamic force generated by the slider 26 and prevents the slider from flying too far off the surface of the disc 22. Although relatively flexible in the vertical direction, the suspension 32 is relatively stiff in the lateral direction in order to provide for precise lateral positioning of the slider 26 over the closely spaced data tracks.
The suspension 32 typically includes a relatively stiff load beam 34 (FIG. 3) and a relatively flexible gimbal 36 for attaching the slider 26. A first or proximal end 38 of the load beam 34 is attached to the arm 30 (FIG. 2) of the rotary actuator 28, and a relatively flexible region 40 (FIG. 3) of the load beam 34 adjacent the actuator arm 30 is typically bent downward toward the surface of the disc 22 to supply the aforementioned preload force. A second or distal end 42 of the load beam 34 opposite the actuator arm 30 is attached (such as by welding) to the more flexible gimbal 36 which, in turn, is fixed to the slider 26. An end of the gimbal 36 includes a cutout region defining two parallel flexure beams 44 and a cross member 45 defining an attachment pad 46. A tongue 48 of the load beam 34 typically protrudes within the cutout region of the gimbal 36 so that a dimple (not shown) on the bottom of the tongue 48 may contact a top surface of the slider 26 to transfer the preload force directly to the slider 26. The attachment pad 46 of the gimbal 36 is secured to the top surface of the slider, such as by an adhesive, so that the flexure beams 44 provide a resilient connection between the slider 26 and the relatively stiff load beam 34. The resilient connection provided by the gimbal 36 is important to allow the slider 26 to pitch and roll (i.e., xe2x80x9cgimbalxe2x80x9d) while following the topography of the rotating disc 22. While FIG. 3 illustrates the load beam 34 and gimbal 36 as separate components, it is understood that these components may be formed from a single piece of metal forming an integrated suspension 32 (not shown).
Although the preload supplied by the bend region 40 of the load beam 34 is effectively countered by the hydrodynamic force generated by the slider 26 during rotation of the disc 22, that same preload force typically forces the slider 26 to rest on the surface of the disc 22 once the disc stops spinning and the hydrodynamic force dissipates (e.g., when the disc drive 20 is powered down). During these periods of inactivity, and particularly during assembly, shipping and handling of the disc drive 20 before the drive is assembled within a computer, the fragile magnetic coating on the surface of the disc 22 is susceptible to damage from accidental vertical displacement of the slider 26, such as by a shock event.
Vertical displacement of the slider 26 may occur when a disc drive 20 is subjected to a shock of sufficient magnitude to cause the actuator arm 30 and the attached suspension 32 to move away from the disc surface (either on the initial shock or on a rebound from the initial shock). Although the bend region 40 in the load beam 34 and the resilient nature of the gimbal 36 tend to hold the slider 26 against the disc surface even as the actuator arm 30 moves away from the disc 22, a sufficiently large shock (e.g., a shock 200 times the acceleration of gravity or 200 xe2x80x9cGsxe2x80x9d) will typically overcome the preload force and cause the slider 26 to be pulled off the disc surface. The return impact of the slider 26 against the disc surface can cause severe damage to the thin magnetic coating on the surface of the disc. If the shock event occurs during operation of the disc drive, the damage to the disc coating may create an unusable portion or sector of the disc and a potential loss of data stored on that portion of the disc. However, most large shock events typically occur during periods of inactivity, as described above, when the slider 26 is positioned along an inner radial portion or xe2x80x9clanding regionxe2x80x9d of the disc 22 not used for data storage. Regardless of whether the impact occurs in the data region or the landing region of the disc 22, the impact typically generates debris particles that can migrate across the surface of the disc 22 and interfere with the air bearing surface of the slider 26, thereby causing damage to more vital regions of the disc 22 during disc operation and possibly leading to a disc xe2x80x9ccrash.xe2x80x9d
Previous efforts to minimize the above described xe2x80x9chead slapxe2x80x9d phenomenon have focused on either increasing the preload force applied by the bend region 40 or reducing the mass of the suspension 32 between the bend region 40 and the head or slider 26. Due to the resiliency of the bend region 40 of the load beam 34, it is primarily the mass of the end portion of the suspension 32 distal to the bend region 40 that determines the lifting force applied to the slider 26 during a shock event. That is, if the force tending to pull the head or slider 26 off the disc surfacexe2x80x94as measured by the acceleration of the shock event (the number of Gs) multiplied by the combined mass of the slider 26 and the portion of the suspension 32 distal to the bend region 40xe2x80x94is greater than the preload force applied by the load beam 34, then the slider 26 will separate from the disc surface resulting in a xe2x80x9chead slapxe2x80x9d as described above. Therefore, a reduction in the mass of the suspension 32 distal to the bend region 40 leads to a reduction in the force applied to the slider 26 during a shock event and thus to improved shock performance for the disc drive 20.
However, reducing the mass of the suspension 32 typically leads to further problems and design compromises. For example, the typical method for reducing the mass of the suspension 32 entails shortening the portion of the suspension between the bend region 40 and the slider 26. However, shortening the suspension tends to increase the variation in the preload force applied by the suspension since the shorter suspension can not typically accommodate variations in the bend angle of the load beam 34 at the bend region 40. In other words, longer suspensions 32 provide lower variations in the preload force resulting from manufacturing tolerances in the bend region 40, while shorter suspensions trade enhanced shock performance for higher variations in the preload force due to these same manufacturing tolerances in the bend angle at the bend region 40. Due to the requirement for careful balancing of the preload force against the hydrodynamic force created by the slider 26, any significant variation of the preload force may cause damage to the fragile surface of the disc 22. Additionally, reducing the mass of the suspension 32 typically reduces the stiffness of the suspension and can adversely affect the tracking performance of the drive 20.
Furthermore, regardless of whether the preload force is increased or the mass of the suspension 32 is decreased, such a xe2x80x9csolutionxe2x80x9d can lead to increased friction and wear problems at the head-disc interface.
It is with respect to these and other background considerations, limitations and problems that the present invention has evolved.
The present invention relates to a disc drive assembly having a suspension that includes a xe2x80x9ccushionxe2x80x9d to protect the slider attached to each suspension by limiting the vertical excursions of the slider and dampening any vibratory motion of the slider when the disc drive assembly undergoes a shock event.
In accordance with one embodiment of the present invention, a suspension is provided for connecting a slider to an actuator arm of a disc drive. The suspension maintains the slider substantially engaged with a disc surface and in one preferred embodiment includes a load beam with a gimbal at a distal end of the load beam. The gimbal is a flexible member that allows limited pitching and rolling motion of the slider while maintaining a stiff connection with the slider in the lateral direction. A xe2x80x9ccushionxe2x80x9d (i.e., a motion limiter and/or dampener) attached to the suspension extends vertically from the suspension. The cushion contacts another surface within the disc drive to limit vertical excursions and to dampen motion of the suspension during a shock event, thereby preventing head slap or at least reducing the severity of a resulting head slap. The cushion may comprise an external feature attached to the suspension, such as a foam or plastic cushion, or may comprise an integral feature of the suspension.
The present invention can also be implemented as a disc drive assembly having at least one disc mounted on a hub for rotation about a spindle axis and an actuator for moving an actuator arm above a surface of a disc. A suspension connects a slider to the actuator arm to maintain the slider substantially engaged with the disc surface. A cushion extends vertically away from the suspension. The cushion defines a contact surface spaced a predetermined distance from an engagement surface within the disc drive, and the contact surface contacts the engagement surface to limit vertical excursions and dampen motion of the suspension when the disc drive undergoes a shock event.
In one embodiment, the engagement surface comprises a contact surface of an adjacent cushion extending vertically from an adjacent suspension. In an alternative embodiment, the engagement surface comprises an adjacent suspension itself so that only a single cushion attached to one suspension separates two adjacent suspensions.
The present invention can further be implemented as a disc drive having a suspension maintaining a slider substantially engaged with a surface of a disc and means for limiting vertical excursions and for dampening motion of the suspension when the disc drive undergoes a shock event.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.